Janus effect-induced asymmetric electron flow in Co nanocluster/NiSe2 heterostructures for efficient bifunctional electrocatalysis.

Herein, we report the rational design of Co nanoclusters decorated on NiSe2 nanoflakes supported on Ni foam (Co@NiSe2) to facilitate the d-band structure modulation and Janus effect via transition metal nanoclusters, which can tune the electronic configuration of electrocatalysts boost water splitting efficiency. The optimized Co@NiSe2 heterostructure exhibits superior bifunctional catalytic activity with outstanding operational durability, delivering overpotentials of only 252 and 360 mV to achieve a current density of 100 mA·cm-2 for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. The symmetric two-electrode electrolyzer using Co@NiSe2 catalyst achieves low cell voltage of 1.49 V at current density of 10 mA·cm-2. To evaluate its practical feasibility, a membrane electrode assembly (MEA) electrolyzer using Co@NiSe2 demonstrates cell voltages of only 2.13 and 2.36 V to reach large-scale relevant current densities of 1.0 and 1.5 A·cm-2. The density functional theory (DFT) calculations for Co@NiSe2 confirm that the Co nanoclusters efficiently tailor the d-band structure of NiSe2 through 3d orbital hybridization and the multivalent nature of cobalt. This electronic modulation induces a profound Janus effect, optimizing the adsorption/desorption energetics for both HER and OER intermediates. Furthermore, in-situ Raman spectroscopy reveals an electrochemical phase transition of the surface into a highly active CoO/NiOOH phase. This work provides a versatile strategy for engineering metal-cluster-based heterostructures to develop efficient electrocatalysts for large-scale, sustainable energy applications.